1. Field of the Invention
This application relates to ventilation of a patient, and, more particularly, to a method and apparatus for invasive ventilation that allows the patient to speak while being ventilated and that detect system anomalies when the ventilator is operating in a speaking mode.
2. Description of Related Art
An example of a known endotracheal tube assembly is disclosed in U.S. Pat. No. 4,759,356 (“the '356 patent”), the entire disclosure of which is hereby incorporated by reference into the present specification. An example of a known ventilator assembly is disclosed in U.S. Pat. No. 6,543,449 (“the '449 patent”), the entire disclosure of which is hereby incorporated by reference into the present specification.
The endotracheal tube assembly disclosed in the '356 patent includes an endotracheal tube configured to be installed into a patient's trachea so that an inner open end communicates with the patient's airway and lungs and an outer open end is suitably anchored exteriorly of the patient's neck. The '356 patent discloses the provision of a check valve on the open end of the tube, often referred to in the art as a “talking valve.” The check valve disclosed in the '356 patent is in widespread use and the '356 patent specification indicates many advantages of the check valve when in use in addition to the basic talking advantage function.
The ventilator assembly disclosed in the '449 patent has the capability of invasive use, as with an endotracheal tube assembly, or non-invasive use, as with a mask. The present invention focuses on the invasive mode of ventilator operation.
As stated in the '356 patent, there are many advantages in addition to the talking capability which result from the use of a check valve. However, there are disadvantages as well. For example, the check valve should be removed in order to give the patient aerosol treatments or to perform suctioning.
U.S. Pat. No. 6,668,824 (“the '824 patent) teaches detecting tubing circuit disconnection and occlusions. The algorithm used in the '824 patent to detect circuit disconnections and occlusions requires detecting the exhalation gas flow during the exhalation phase of a breath, i.e., detecting the flow of gas traveling through the expiratory limb of the patient circuit during exhalation. The exhalation flow, in combination with at least one other monitored parameter, such as exhalation pressure, is used to detect circuit disconnections and occlusions. This technique, however, cannot be used if the ventilation mode implemented by the ventilator specifically avoids or does not require a flow of gas in the expiratory limb during exhalation.